Sheet stacker

ABSTRACT

A lift table is movably mounted on a frame adjacent to one end of a conveyor belt which deposits sheets of corrugated board or the like on the lift table. As the sheets pile up on the lift table, the table is automatically lowered so that the top of the stack remains below the level of the conveyor belt. When the stack reaches a predetermined height, the conveyor belt is blocked to interrupt the delivery of sheets, and the stack is moved off the lift table by live rollers thereon. The lift table is then raised at a relatively high speed to the level of the conveyor belt, which is subsequently unblocked to start a new stack. The lift table has a pair of torsion bars journalled to opposite sides of the lift table parallel to the table top. Four pairs of sprockets are rigidly attached to the corresponding ends of the torsion bars. Two pairs of leveling chains are attached at both ends to the frame and operatively engage corresponding sprockets to rotate the torsion bars and maintain the lift table level as it is raised and lowered. The lift table is raised and lowered by hydraulic cylinders which are linked to the lift table by chains. The hydraulic cylinders are mounted within the upper frame members to conserve space.

SHEET STACKER BACKGROUND OF TI-IE INVENTION This invention relates to sheet stackers such as used in combination with corrugator machines or the like to stack the output of `the machine in neat stacks and move the stacks away from the machine.

One object of the invention is to provide a sheet stacker having a relatively large lift table which is maintained in a level attitude throughout its range of travel by an automatic leveling mechanism. Another object of the invention is to provide a sheet stacker in which the lift table may be emptied and repositioned fast enough to obviate stopping the machine which supplies the sheets to be stacked.

A further object of the invention is to provide a sheet stacker which is compact in structure and requires a minimum of space.

`Other objects and advantages of the invention will become apparent to those skilled in the art from the description which follows.

SUMMARY OF THE INVENTION A lift table is movably mounted for upward and downward movement on a frame to receive and stack sheets from an adjacent conveyor belt or the like. The lift table is raised by hydraulic cylinders which are linked to the table. The hydraulic cylinders are mounted within the upper frame members to conserve spaceA The cylinders are bled to lower the lift table as the stack of sheets grows. After the stack reaches a predetermined height, the input of sheets is blocked, and the stack is moved off the lift table, which is then moved upward at a relatively high speed until it is in position to receive a new stack. At least one and preferably two torsion bars are journalled to opposite sides of the lift table parallel to the table top. Four pairs of sprockets are each rigidly attached to corresponding ends of the torsion bars. At least one and preferably two pairs of leveling chains are attached at both ends to the frame and operatively engage corresponding sprockets to rotate the torsion bars and maintain the lift table level as it is raised and lowered.

DESCRIPTION OF THE DRAWINGS FIG. l is a diagrammatic perspective view of one illustrative embodiment of the invention;

FIG. 2 is a longitudinal sectional view of the embodiment diagrammatically represented in FIG. 1; and

FIG. 3 is a detail cross-sectional view taken on the line 3-3 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 2, one embodiment of this invention is mounted within a frame l which includes four upright posts 12 which are positioned in a rectangular pattern and are joined together on their upper ends by four cross beams 14 which each extend between the upper ends of two corresponding upright posts 12. The lower corners of the upright posts 12 are joined together by two channel members 16 which extend parallel toeach other between two adjacent corners of upright posts 12. The space between the bottom ends of the upright posts 12 transverse to the channel members 16 is left open to allow a lift table which is described hereinafter to be lowered to the bottom of the frame 10 for unloading the cardboard sheets stacked thereon.

A lift table 18 is movably mounted within the frame l0 for upward and downward movement therewithin. The lift table 18 has a rectangular base formed by four lower channel members 20 which are welded together at their corners. Two parallel side channel members 22 are joined to opposite sides of the lower channel members 20. A plurality of rollers 24 is journalled between the two channel members 22 to provide a rollable upper surface for the lift table 18. Sprockets 26 are rigidly coupled to one end of every other roller 24 for driving alternate rollers to move a stack of cardboard sheets off the top of the lift table 18 as will be described hereinafter. The lift table 18 fits within the interior of the frame 10 and is supported by a pair of lift chains 28 whose bottom ends 30 are attached to the diagonallyopposite corners of the side channels 22 (see FIG. l The chains 28 extend upwardly from the corners 30 and are directed in a horizontal direction at the top of the frame 1Q by idler sprockets 32. The upper end of each chain 2,8 is fastened at a convenient point to the frame 10 and extends around another idler sprocket 34 which is attached to the piston shaft 36 of a hydraulic cylinder 38. To conserve space, the hydraulic cylinders 38 are mountedwithin frame 10 as shown in FIG. 3.

TheA hydraulic cylinders 38 are provided with hydraulic fluid under pressure through hydraulic conduits 40 which receive hydraulic fluid from a three-way hydraulic valve 42. The hydraulic valve 42 is a solenoid valve which is electrically operated by suitable electrical control signals froma control Circuit 44. In one position of the hydraulic control valve 42, hydraulic fluid under pressure is applied to the hydraulic conduits 40 to cause the hydraulic pistons 36 to move toward the corresponding lhydraulic cylinders 38. This draws the chains 28 upward and thereby raises the lift table 18. In a second-position of the hydraulic valve 42, the hydraulic fluid within the cylinders 38 and hydraulic conduits 40 is blocked off to hold the lift table 18 in the same position'. In the third position of the hydraulic valve 42, hydraulic fluid is bled out of the conduits 40 and cylinders 38 via a hydraulic exhaust conduit 4S to a hydraulic reservoir. This lowers the chains 28 and thereby lowers the lift table 18.

The hydraulic fluid for the hydraulic valve 42 is applied via a hydraulic conduit 46 which receives hydraulic fluid from one or both of two hydraulic pumps 48 and 50 which are driven by an electric motor 5l. The pump 48 is a relatively low capacity pump used for moving the lift table 18 at a relatively low speed and the pump 50 is a relatively high capacity pump which is used to raise the lift table 18 at a relatively high rate of speed for reasons which will be discussed hereinafter. The hydraulic pumps 48 and 50 are coupled to the hydraulic conduit 46 through two solenoid valves S2 and 54 which are controlled by signals from the control circuit 44. The hydraulic pumps 48 and 50 are coupled to thehydraulic reservoir through hydraulic conduits 56 and 58.l

The hydraulic pumps 48 and 50 are also coupled via a solenoid valve 60 to a hydraulic motor 62 which is mounted on the frame as shown in FIG. 2. Hydraulic motor 62 drives a chain 64 which engages the sprockets 26 on rollers 24 as shown in FIG. 1. Every other sprocket 26 is an idler. The chain 64 is Snaked through the sprockets 26 and is doubled back over an idler sprocket 66 which is rotatably attached to the bottom of the channel member so that it moves along with the lift table 18. From idler sprocket 66, the chain 64 passes around another idler sprocket 68, which is rotatably attached to the frame 10, and then returns to the drive sprocket on motor 62. When the motor 62 is energized, it drives the chain 64 and causes every other roller on the lift table 18 to be rotated in the same direction to move a stack of sheets off the lift table 18 as will be described hereinafter.

Since the lift table 18 is relatively large, and may receive an unbalanced stack of sheets such as illustrated in FIG. 2, it is desirable to provide an automatic levelingV means for holding the lift table 18 level as it moves throughout its range of upward and downward travel. In accordance with this invention, such automatic leveling means includes at least one and preferably two torsion bars 70 which are journalled through the channel members 20 on opposite sides of the lift table 18 and project laterally therefrom. Two sprockets 72 and 74 are rigidly'attached to both ends of both torsion bars 70 as shown in FIG. l. The inner sprockets 72 are operatively engaged with an inner leveling chain 76 which is attached at both ends to the frame 10 and extends between the two sprockets 72, passing around the underside of the rear sprocket 72 and passing over the top side of the forward sprocket 72. The upper end of inner leveling chains 76 are attached to frame 10 at attachment points 78 which are located above the rear sprockets 72. The lower ends of the inner leveling chain 76 are attached to the frame 10 at attachment points 80 which are located below the corresponding forward sprockets 72. A pair of outer leveling chains 82 is attached at both ends to the frame 10 on opposite sides thereof and extend between the two outer leveling sprockets 74, the chain 82 passing under the front sprocket 74 and passing over the rear sprocket 74. The upper ends of the chains 82 are attached to the frame 10 at attachment points 84 which are positioned above the corresponding front outer sprockets 74. The bottom of the chains 82 are attached to the frame 10 at attachment points 86 which are located under the outer rear sprocket 74.

Adjustment means may be attached to chains 76 at points 78 and to chains 82 at points 84 to permit the lift table 18 to be manually leveled.

The above described torsion bars 70, sprockets 72 and 74, and leveling chains 76 and 82 act to keep all four corners of the lift table 18 at the same level throughout its range of upward and downward travel. If any one of the corners should drop or rise with respect to the other corners, this drop or rise will be communicated through the torsion bars 70 to the other side of the lift table and through the chains 76 and 82 to both of the other corners of the lift table 18 so that an upward or downward movement of any one corner will cause an equal upward or downward movement on all of the three remaining corners so that the four corners of the lift table 18 will always move in synchronism and thereby maintain the table in a level condition even if an unbalanced load is applied thereto.

Referring to FIG. 2, a conveyor belt 88 carrying sheets 90 of paperboard, cardboard, corrugated board or the like enters the upper portion of the cubical frame 10 and deposits the sheets in a stack 92 on the top of the lift table 18. A sheet stop member 94 serves to limit the forward movement of the sheets 90 so that they form an even stack. A photocell and light source 96 and mirror 98 (see FIG. 1) are attached to opposite ends of the stop member 94 and serve to generate a signal that causes the lift table 18l to be lowered as will be described hereinafter. The stop member 94 and the photocell 96 and mirror 98 are all attached to a rack and pinion gear 100 by means of which the height of the photocell 96 and its reflecting mirror 98 may be raised and lowered for alignment purposes. The distance between the stop member 94 and the end of conveyor belt 88 may also be made adjustable if desired to accommodate different size sheets in the stacker.

As the sheets 90 approach the end of the conveyor belt 88, they engage rubber idler rollers 102 which press the sheets downward onto the upper surface of conveyor belt 88 to prevent slippage between the upper surface ofthe conveyor belt 88 and the sheets 90 at the point where they are pushed onto the top of the stack 92. A movable gate member 104 is mounted in front of the idler rollers 102. Gate member 104 is normally spring biased upwardly by a spring 106 but can be pulled downward to block the entry of the sheets 90 into the sheet stacker by means of a solenoid 108. The gate 104 is lowered at the end of an operating cycle to block the entry of sheets 90 into the sheet stacker at a time when the stack 92 is being removed therefrom.

Referring to FIG. 2, an operating cycle 0f the abovedescribed sheet stacker will be described starting with the condition illustrated in FIG. 2 in which the sheets 90 are being deposited on the stack 92. As the sheets 90 pile up on the stack 92, they block the beam of light between photocell and light source 96 and mirror 98, which develops an electrical signal that is applied to the control circuit 44. The control circuit 44 then actuates the valve 42 to bleed some of the hydraulic fluid out of the cylinders 38, thus lowering the lift table 18 andthe stack 92 until the beam of light from the photocell 96 to the mirror 98 is unbroken again. This lowering of the stack 92 is repeated periodically as the sheets pile up with the effect that the stack 92 grows taller and the lift table 18 approaches the bottom of the frame l0.

Near the bottom of the frame 10, the lift table 18 engages a microswtch which is electrically coupled to the control circuit 44. The control circuit 44 then sends an electrical signal to the input gate solenoid 108 to draw the gate 104 downward against the upward pressure of spring 106 to halt the inward movement of sheets 90. The circuit then waits for a predetermined delay time to allow the last sheet 90 to reach the stop member 94 and complete the stack 92. Thereafter, the control circuit 44 opens the solenoid valves 52 and 60 to couple the low capacity hydraulic pump 48 to the hydraulic motor 62 and initiate relatively slow drive on the rollers 24 under the stack 92 via the chain 64 and the sprockets 26. The stack 92 then begins to move sideways out of the sheet Stacker and onto a pallet or conveyor which is placed at the side of the frame l0 to receive the stack 92. After a short time delay to allow the stack 92 to begin moving relatively slowly out of the side of the sheet stacker. the control circuit 44 opens the solenoid valve 54 to increase the amount of hydraulic fluid driven through the motor'62 to raise the rotary speed of the rollers 24 in order to remove the ystack 92 from the lift table 18 in a' relatively short period of time. This two-speed feature is an important feature of the invention because the stack'92 must be removed from the lift table 18 in as short a time-period s possiate to avoid having to' shut down the Conveyor 88 at the'i'nput of the machine or the equipment vsuchafs'a corrugat'or machine which is coupled to 'the joi'iveyo'l` belt: I88. Since the stack V92 is relatively large," it must beinitially moved relatively slowly, but after it is starteda Iit iis highly desirable to move it at a faster speed to reduce the unloading time for the machine. i' y After a predetermined time delay to allow the stack 92 to be completely driven off of the lift table 18,1the solenoid valve 60 is closed to terminate the drive on the rollers 24 and the solenoid valve 42 is opened to begin moving the lift table 18 upwardly. At this time the solenoid valves 52 and 54 are both open and therefore a relatively high volume of hydraulic fluid pours into the cylinders 38 to raise the lift table 18 at a relatively high rate of speed. As the lift table 18 approaches the end of conveyor belt 88, it closes a microswitch 112 which is wired to the control circuit 44. The closing of microswitch 112 causes the control circuit 44 to switch the solenoid valve 54 off and block the high capacity hydraulic pump 50, thereby substantially reducing the speed at which the lift table 18 is raised. The lift table 18 then continues to move upward at a slow rate until it strikes the bottom of the stop member 94, which mechanically blocks the lift table 18 from rising any further. The solenoid valve 52 is subsequently closed to remove the hydraulic drive and the solenoid valve 42 is ope rated in the state to hold the hydraulic fluid in the conduits 40 and cylinders 38 so as to hold the lift table 18 in position. The solenoid 108 is then released and the gate member 104 is lifted to allow the sheets 90 to again pile up on the lift table 18.

The above described cycle is repeated for the next stack 92 which is accumulated on lift table 18.

We claim:

l. ln a sheet stacker having a frame, a table and means for moving the table up and down with respect to the frame, the improvement for leveling the table regardless of unbalanced loads thereon and Comprising a first torsion bar at one side of the table, a second torsion bar at the opposite side of the table, pairs of sprockets fixed at both ends of both torsion bars, pairs of leveling chains at both ends of said torsion bars, anchor means anchoring each such chain to the frame above the table, said chain extending downwardly from its said anchor means and around the bottom of a sprocket on an end of a torsion bar and thence laterally across the table and around the top of a sprocket on an end of a torsion bar at the other side of the table and thence downwardly and means anchoring the chain to the frame below the table whereby unbalanced forces tending to tilt the table will be transmitted by said torsion bars from one side of the table to the other to tend to balance said forces and maintain the table level` corresponding chains of each pair of chains being anchored to the frame above the table and above the ends of said first torsion bar at said one side of the` table and other corresponding chains of each pair of chains being anchored to the frame above the table and above the ends of said second torsion bar at said opposite side of said table, the'chains of each pair having side-by-side runs extending across the table.

2.'The improvement of claim l in which said pairs of sprockets vinclude an inner sprocket and outer sprocket,` one chain of each pair being trained around inner sprockets on the ends of said torsion bars and the otherchain of each pair being trained around outer sprockets on the ends of said torsion bars.

3.jlna sheet stacker having a frame and having a lift table'movably mounted on the` frame for upward and downward movement, and having means for raising and vlowering the lift table, the improvement comprising two torsion bars each joumaled to opposite sides of sai'd lift table and extending thereacross, inner and outer sprockets rigidly attached to each end of each torsion bar, a first leveling chain rigidly attached at one end to said frame above one comer of said lift table and rigidly attached at the other end to said frame below an opposite comer of said lift table, said first leveling chain being entrained under the inner sprocket at one end of one torsion bar and being entrained over the inner sprocket at the corresponding end of the other torsion bar, a second leveling chain rigidly attached at one end to said frame above the bottom end of said first leveling chain and rigidly attached at the other end to said frame below the upper end of said first leveling chain, said second leveling chain being entrained over the outer sprocket of said one torsion bar and being entrained under the outer sprocket of said other torsion bar, a third leveling chain rigidly attached at one end to said frame above the other end of said one torsion bar and rigidly attached at the other end to said frame below the other end of said other torsion bar, said third leveling chain being entrained under the inner sprocket at the other end of said one torsion bar and being entrained over the inner sprocket at the other end of said other torsion bar, and a fourth leveling chain rigidly attached at one end to said frame under the upper end of said third chain and rigidly attached at the other end to said frame over the lower end of said third chain, and said fourth leveling chain being entrained over the outer sprocket of said one torsion bar and being entrained under the outer sprocket of said other torsion bar, thereby equalizing upward and downward forces applied to any portion of said lift table.

4. In a sheet stacker having a frame and having a lift table movably mounted on the frame for upward and downward movement, and having means for raising and lowering the lift table, the improvement wherein said means for raising said lift table includes at least one hydraulic cylinder coupled to said lift table and pump means for forcing hydraulic fluid into said cylinder to raise said lift table, said pump means including a relatively high capacity pump for raising said lift table at a relatively high speed and a relatively low capacity pump for raising said lift table at a relatively low speed, a plurality of rollers joumaled to said lift table and forming the upper surface thereof, a plurality of sprockets coupled to alternate rollers, a drive chain operatively engaged with said sprockets for driving the rollers coupled thereto, a hydraulic motor operatively engaged with said drive chain for driving the same, and hydraulic valve means selectively coupling said low capacity purnp to said hydraulic motor to drive the motor at a relatively low speed and selectively coupling said high capacity pump to said hydraulic motor to drive the motor at a relatively high speed.

5. The sheet stacker defined in claim 4 wherein said hydraulic motor is mounted on said frame above a corner of said lift table, and further comprising a loop in said drive chain extending downwardly from said hy'- draulic motor to said roller sprockets, an idler sprocket journal to said frame below said corner of said lift table, and a second loop in said drive chain extending downwardly from said roller sprockets to said idler sprocket, whereby movement of said drive chain will drive said roller sprockets regardless of the vertical position of said lift table.

6. The sheet stacker defined in claim 5 and further comprising a second idler sprocket journaled to said lift table above the first mentioned idler sprocket and below said rollers, said drive chain being entrained over said second idler sprocket and extending downwardly from said second idler sprocket to said first mentioned idler sprocket, said drive chain extending upwardly from said first mentioned idler sprocket to said hydraulic motor and extending downwardly from said hydraulic motor to said roller sprockets.

7. The sheet stacker defined in claim 4 wherein said hydraulic valve means includes a first valve coupled in series with said high capacity pump but not said low capaci'ty pump, a second valve coupled in series with said low capacity pump but not said high capacity pump, a third valve coupled in series with both said first and second valves between said first and second valves and said hydraulic cylinder for raising said lift table, and a fourth valve coupled in series with both said first and second valves between said first and second valves and said-hydraulic motor, whereby said high capacity pump and low capacity pump can be selectively coupled to said hydraulic cylinder for raising said lift table at a selected one of two speeds and can be selectively coupled to said hydraulic motor for rotating said rollers at a selected one of two speeds. 

1. In a sheet stacker having a frame, a table and means for moving the table up and down with respect to the frame, the improvement for leveling the table regardless of unbalanced loads thereon and comprising a first torsion bar at one side of the table, a second torsion bar at the opposite side of the table, pairs of sprockets fixed at both ends of both torsion bars, pairs of leveling chains at both ends of said torsion bars, anchor means anchoring each such chain to the frame above the table, said chain extending downwardly from its said anchor means and around the bottom of a sprocket on an end of a torsion bar and thence laterally across the table and around the top of a sprocket on an end of a torsion bar at the other side of the table and thence downwardly and means anchoring the chain to the frame below the table whereby unbalanced forces tending to tilt the table will be transmitted by said torsion bars from one side of the table to the other to tend to balance said forces and maintain the table level, corresponding chains of each pair of chains being anchored to the frame above the table and above the ends of said first torsion bar at said one side of the table and other corresponding chains of each pair of chains being anchored to the frame above the table and above the ends of said second torsion bar at said opposite side of said table, the chains of each pair having side-by-side runs extending across the table.
 2. The improvement of claim 1 in which said pairs of sprockets include an inner sprocket and outer sprocket, one chain of each pair being trained around inner sprockets on the ends of said torsion bars and the other chain of each pair being trained around outer sprockets on the ends of said torsion bars.
 3. In a sheet stacker having a frame and having a lift table movably mounted on the frame for upward and downward movement, and having means for raising and lowering the lift table, the improvement comprising two torsion bars each journaled to opposite sides of said lift table and extending thereacross, inner and outer sprockets rigidly attached to each end of each torsion bar, a first leveling chain rigidly attached at one end to said frame above one corner of said lift table and rigidly attached at the other end to said frame below an opposite corner of said lift table, said first leveling chain being entrained under the inner sprocket at one end of one torsion bar and being entrained over the inner sprocket at the corresponding end of the other torsion bar, a second leveling chain rigidly attached at one end to said frame above the bottom end of said first leveling chain and rigidly attached at the other end to said frame below the upper end of said first leveling chain, said second leveling chain being entrained over the outer sprocket of said one torsion bar and being entrained under the outer sprocket of said other torsion bar, a third leveling chain rigidly attached at one end to said frame above the other end of said one torsion bar and rigidly attached at the other end to said frame below the other end of said other torsion bar, said third leveling chain being entrained under the inner sprocket at the other end of said one torsion bar and being entrained over the inner sprocket at the other end of said other torsion bar, and a fourth leveling chain rigidly attached at one end to said frame under the upper end of said third chain and rigidly attached at the other end to said frame over the lower end of said third chain, and said fourth leveling chain being entrained over the outer sprocket of said one torsion bar and being entrained under the outer sprocket of said other torsion bar, thereby equalizing upward and downward forces applied to any portion of said lift table.
 4. In a sheet stacker having a frame and having a lift table movably mounted on the frame for upward and downward movement, and having means for raising and lowering the lift table, the improvement wherein said means for raising said lift table includes at least one hydraulic cylinder coupled to said lift table and pump means for forcing hydraulic fluid into said cylinder to raise said lift table, said pump means including a relatively high capacity pump for raising said lift table at a relatively high speed and a relatively low capacity pump for raising said lift table at a relatively low speed, a plurality of rollers journaled to said lift table and forming the upper surface thereof, a plurality of sprockets coupled to alternate rollers, a drive chain operatively engaged with said sprockets for driving the rollers coupled thereto, a hydraulic motor operatively engaged with said drive chain for driving the same, and hydraulic valve means selectively coupling said low capacity pump to said hydraulic motor to drive the motor at a relatively low speed and selectively coupling said high capacity pump to said hydraulic motor to drive the motor at a relatively high speed.
 5. The sheet stacker defined in claim 4 wherein said hydraulic motor is mounted on said frame above a corner of said lift table, and further comprising a loop in said drive chain extending downwardly from said hydraulic motor to said roller sprockets, an idler sprocket journal to said frame below said corner of said lift table, and a second loop in said drive chain extending downwardly from said roller sprockets to said idler sprocket, whereby movement of said drive chain will drive said roller sprockets regardless of the vertical position of said lift table.
 6. The sheet stacker defined in claim 5 and further comprising a second idler sprocket journaled to said lift table above the first mentioned idler sprocket and below said rollers, said drive chain being entrained over said second idler sprocket and extending downwardly from said second idler sprocket to said first mentioned idler sprocket, said drive chain extending upwardly from said first mentioned idler sprocket to said hydraulic motor and extending downwardly from said hydraulic motor to said roller sprockets.
 7. The sheet stacker defined in claim 4 wherein said hydraulic valve means includes a first valve coupled in series with said high capacity pump buT not said low capacity pump, a second valve coupled in series with said low capacity pump but not said high capacity pump, a third valve coupled in series with both said first and second valves between said first and second valves and said hydraulic cylinder for raising said lift table, and a fourth valve coupled in series with both said first and second valves between said first and second valves and said hydraulic motor, whereby said high capacity pump and low capacity pump can be selectively coupled to said hydraulic cylinder for raising said lift table at a selected one of two speeds and can be selectively coupled to said hydraulic motor for rotating said rollers at a selected one of two speeds. 